Apparatus for measuring the maximum values of alternating current voltages



C. H. SHARP.

APPARATUS FOR MEASURING THE MAXIMUM VALUES 0F ALIERNATING CURRENTVOLTAGES.

APPLICATION FILED OCT. 26. 19:4.

1,209,76. I Patented Dec. 26,1916.

Mrwemm Witnesses A ttorneys.

APPARATUS FOR MEASURING THE MAXIMUM VALUES OF ALTERNATING-CURRENTVOLTAGES.

To all whom it may concern:

Be it known that I, OLAY roN I-I. SHARP, a citizen of the United States,residing in White Plains, county of Westchester, and State of New York,have invented a certain new and useful Apparatus for Measuring theMaximum Values of Alternating-Gurrent Voltages, of which the followingis a specification.

L The object of this invention 1s to furnlsh an apparatus for measuringdirectlythe maximum or peak or crest value of alternatvoltmeter givesthe effective or root-meansquare value of alternating voltages. For

- certain purposes it is desirable to know the stz'tate of maximum orpeak or crest value of the alternating voltage wave, notably testlng1nsu.- lating materials for dielectric strength or puncture value, whereit is prdbaloly the maxlmum value which causes the break-down,

and where the ratio of the maximum or peak or crest value to theroot-mean-square value as indicated by the ordinary voltmeter depends onthe wave form, a quantity which is often subject to variation arisingout of the conditions of the test itself. One means of measuring peakvoltage values has been pointed out by Sharp and Farmer who have alsogiven a method whereby they may be measured. See Transactions Americanln- E'Zectm'cal Engineers, June 28, 1912, pages 1237 to 1242.

In the drawings, Figure 1 showsa diagram of one of the arrangementswhereby the invention is carried out; and Fig. 2 showsthe voltage andcurrent waves in the apparatus.

In both of the views, like parts are designated by the same referencecharacters.

In Fig. 1: 1 is an electrometer or electrostatic voltmeter. 2 is acondenser in parallel with the same. 3' is the source of alternatingvoltage to be measured. 4 is a glass bulb of a hot cathode valve orrectifier. 5 is the anode. 6 is the hot cathode. 7 is thesecondarywinding of a step-down transformer supplying current to heat theoathode. 8 is the primary winding of said transformer. The variousconnecting and leading-in wires are as shown.

In Fig. 2:, 9 is the alternating, voltage wave. 10 is the current wavepassing into the condenser and voltmeten' The valvecondenser andstep-down transformer may Specification of Letters Patent.

Application filed October 26, 19151. Serial No. 868,679.

ing voltages. The ordinary alternating oiiricn.

CLAYTON H. SHARP, or WHITE Prams, NEW YORK.

Patented Dec. at, 1am.

be inclosed in the voltmeter case, if so desired.

In the-present invention advantage is taken of the known property of asuitable electric valve or rectifier to charge acondenser to the peakvalue of an alternating Wave. An electric valve is an apparatus allowingcurrent to pass principally in one direction. Electric valves have beenconstructed and described which will permit current to flow freely inone direction and will absolutely prohibit its passage in the oppositedirection except with very high voltages. Such an apparatus is shown inFig. 1. If a valve of this sort is placed in series with anelectrostatic voltmeter connected across an alternating line, therelations of voltage and cur- .rent will be such ,During the firstquarter cycle of voltage 9, current 10" will flow into the voltmeter.This as are shown in Fig. 2.

current will cease as soon as the voltage has attained its maximum orpeak value and the charge remains on the voltmeter because of theinability of .the current to flow in the opposite directionthrough thevalve. If

the flow of current through the valve during the first quarter cycle hasnot been sufficient to raise the. potential of the voltmeter to the fullpeak voltage of the wave a certain amount of current will flow into thevoltmeter during the fifth quarter cycle of the voltage wave andsimilarly a smaller amount may fiow during the ninth, thirteenth, etc,quarter cycles until the potential of. the voltmeter has become the sameas that of the eak of the voltage wave. Thereafter no current will flowexcept such as may be necessary to supply the leakage from the voltmeterand connected apparatus shown. This, with a well constructed apparatus,may be made very'small.

It is found that it is desirable to place a condenser having aconsiderably larger electrostatic capacity than that of the ordinaryapparatus in parallel with the voltmeter in order to serve as a storagereservoir of charge'and to prevent any undue loss in the voltmeterpotential due to leak age in the interval between two successive peaksduring which a charging current may flow. Both the condenser andvoltmeter then become charged to the maximum voltage of the wave and thevoltmeter will read this value in volts. If, when this condition hasbeen obtained, the voltage on the line is for any reason reduced as forexample, by the puncture of lnsulating material under test,

the voltmeter needle will retain its maximum position dropping backtoward zero slowly at a rate which depends upon the capacity and uponthe leakage. Therefore,

, in testing with this apparatus it is not necesvalve is short circuitedthe voltmeter at once drops-back to indicate the root-meansquare valueof the alternating-wave. Thus the apparatus becomes useful indetermining the crest factor of alternating waves which is the ratio ofthe peak or crest voltage to the root-mean-square voltage. This is asimple means of determining whether an unknown wave is peaked orfiat-topped in form.

While I have illustrated my invention in connection with anelectrostatic voltmeter, I desire to have it understood that I do notwish to limit myself to such a construction as various other measuringdevices may be employed. An electrostatic voltmeter combines in itself acondenser and a voltage measuring device. A practical equivalent formany purposes is an ordinary-condenser with an electromagnetic measuringdevice having a high. electrical resistance.

Having described my invention, what I claim as new and desire to secureby Letters Patent, is:

1. The combination with an alternating line, of an electrostaticvoltmeter connected across the same, and an electric valve in serieswith and voltmeter.

2. The combination with an alternatlng line, of an electrostaticvoltmeter connected. across the same, a condenser 1n parallel with j thevoltmeter, and an electric valve in; series with said voltmeter.

3. Anapparatus for measuring the maxi mum values of alternating currentvoltages, which includes an electric valve in series with anelectrostatic measuring instrument.

4. An apparatus for measuring the maximum values of alternating currentvoltages,

which includes an electric valve in series mum values of alternatingcurrent voltages, WhlCll comprises an electrostatic voltmeter connectedacross the line, and a recti g device in series with said'voltmeter, saidevice including an anode and a cathode, and means for heating thelatter.

'7. An apparatus for measuring the maximum values of alternating currentvoltages, which comprises an electrostatic voltmeter connected acrossthe line, and a rectifying device in series with said voltmeter, saiddevice including an anode and a cathode, means for heating the latter,and a condenser in parallel with said voltmeter.

This specification signed and witnessed this nineteenth day ofSeptember, 1914:.

I CLAYTON H. SHMP.

. Witnesses:

J. H. KINTAND, Gnonen KI'iHNnR.

